The present invention relates to a power change operating method of a boiling water reactor.
The power change of a boiling water reacter (hereinafter referred to as a BWR) can be realized by a control rod operation by a core flow changing operation. The present invention will be described as to the power change driving operation resorting mainly to the core flow. Between this core flow and the thermal power, an operation allowable range is predetermined. The operation allowable range is defined by a minimum pump speed line of recirculation pump speed, an APRM rod block monitor line by the thermal restriction of a fuel assembly, a minimum power line relating to pump cavitation, and a 100% pump speed line of the recirculation pump speed. During the power change, there arises a change in the concentration of a fission product or xenon. Since the concentration change of xenon results in a considerable change in reactivity, the core flow has to be greatly changed in order to maintain the thermal power after the change constant. The change in the core flow under a low power condition raises no problem because it is in a direction apart from the restricting value. Under a return condition to a high power, there is possibility of the power going out of the operation allowable range. According to the conventional operating method, whether an operation restricting condition is violated or not has been judged on the basis of the analytical results of an off-line calculation or the operational experiences of the operator with the use of a power-flow map.